Do today’s kids make terrible entry-level workers? That’s a question much on employers’ minds as graduation season kicks off and young adults begin their first full-time jobs. We’ve all heard the stories: assistants who won’t assist, new workers who can’t set an alarm, employees who can’t grasp institutional hierarchies.

Bosses who toiled in the pre-self-esteem era salt mines have little patience for these upstarts. A popular advice columnist had some choice words last week for a young employee who dismissively waved her sandwich at a superior requesting backup during a critical meeting; the young woman explained that she was on her lunch break and was merely “setting boundaries” with a “disrespectful colleague who sorely needs them.” Moreover, she noted, being “errand girl” wasn’t in her job description.

It’s easy to laugh off these anecdotes, but there are some complex reasons for the lack of familiarity with work norms. For one thing, many 20-something adults have never held a menial summer job, once considered training wheels for adult life in the American middle class.

It was once common to see teenagers mowing lawns, waiting tables, digging ditches and bagging groceries for modest wages in the long summer months. Summer employment was a social equalizer, allowing both affluent and financially strapped teenagers to gain a foothold on adulthood, learning the virtues of hard work, respect and teamwork in a relatively low-stakes atmosphere. But youth employment has declined precipitously over the years, and young people are losing a chance to develop these important life skills in the process.

In 2010, the latest year for which numbers are available, less than half of the nation’s youths (ages 16 to 24) were employed during the month of July, traditionally the peak of summer employment, the lowest percentage since the Bureau of Labor Statistics started collecting data in 1948 and almost 20 points lower than the peak in 1989. There’s little indication of that number improving. Teenagers and 20-somethings are the least skilled and most expendable members of the workforce, so it’s not surprising that they would be edged out in a recession by more reliable full-time workers such as senior citizens, immigrants and other adults who need those jobs.

But other long-term factors are at play. Life is more competitive than ever before, and kids — or perhaps their parents — worry about wasting time on jobs that won’t yield career dividends. On Harvard’s campus, where I work, students feel crushing pressure to build their résumés the instant they arrive, eschewing unskilled summer jobs for unpaid internships with nonprofit organizations, political campaigns and research labs. Others spend the summer studying foreign languages or preparing for grueling graduate-admissions exams.

The same pattern is found at the secondary-school level, where teen employment has been on a downward trend since 2000. Tougher graduation standards have created a threefold increase in summer-school attendance over the past 20 years. And students feel the need to pad their college applications with unique life experiences as the admissions process has grown more selective. High schools also now routinely require public service — surely a good thing — that can further limit the available hours to work for pay.

Many of these social changes are a sign of a healthy, and upwardly mobile, society. But there’s a problem when more than 50% of the nation’s young workforce has never held a basic, paying job. We may be postponing their entry into adulthood. One paradox of contemporary life is that the lengthening of adolescence has not better prepared young people for what comes next. Despite unprecedented technological and cultural sophistication, this generation’s 20-year-olds lack some of the soft skills that are necessary to move up the professional ladder: perseverance, humility, flexibility and commitment.

In the end, though, it’s their elders who are responsible, and we shouldn’t demonize young people for our own failings. Most graduates embarking on their first job are eager to perform well and desperately need the income. It’s grownups, not teenagers, who have honed the values, expectations and opportunities from which our nation’s youth develop their work habits. If we want a more respectful and industrious workforce, we need to do a better job creating one.